Field of the Invention
The present invention relates to a solid-state image pickup apparatus, and more particularly, to a technology of reducing a reading error of a pixel signal.
Description of the Related Art
As one of shutter methods suitable for a solid-state image pickup apparatus using a CMOS image sensor, an electronic shutter method is known. With the electronic shutter method, timing of resetting signal charges, which are photoelectrically converted and accumulated in a photodiode in a pixel, is controlled to achieve variable accumulation time of the signal charges.
With the electronic shutter method, the signal charges in the pixels arranged in a matrix are sequentially reset for each row in synchronization with a horizontal synchronization signal. Then, the signal charges accumulated in each of the pixels are sequentially read for each row after elapse of an accumulation period. A length of the accumulation period is normally the same for each row when a horizontal period corresponding to an interval between the horizontal synchronization signals is constant. When a cycle of a vertical period is not an integer multiple of a cycle of the horizontal synchronization signal, however, an odd period in the vertical period is adjusted in a specific row. As a result, a difference in length of the accumulation period between the rows increases to disadvantageously generate flicker noise or the like.
With a technology described in Japanese Patent Application Laid-Open No. 2012-129634, an interval between the horizontal synchronization signals is adjusted to disperse an odd-period adjustment period within the vertical period so as to prevent the difference in length of the accumulation period between the rows from increasing.
In a solid-state image pickup apparatus, the pixel signal is read based on the charges photoelectrically converted in the pixel, in synchronization with the horizontal synchronization signal. Meanwhile, due to increase in the number of pixels and increase in frame rate of the solid-state image pickup apparatus in recent years, the cycle of the horizontal synchronization signal is shortened. With reduction in the cycle of the horizontal synchronization signal, time required to stabilize the pixel signal output to an output line relatively increases. As a result, there arises a case where a transition is not completed before the start of reading of the pixel signal.
When the interval between the horizontal synchronization signals differs between the rows as in the technology described in Japanese Patent Application Laid-Open No. 2012-129634, a state of convergence of the pixel signal at reading timing differs between the rows. Thus, there is a problem in that a reading error of the pixel signal disadvantageously occurs.